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Quality Indicators of Rice Based Gluten-free Bread-like Products: Relationships 1
between Dough Rheology and Quality Characteristics 2
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1) Short running head: Rice based gluten-free bread like products 4
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2) First name, middle initial, last name of each author: 6
María Estela Matos1,2, Cristina M. Rosell1* 7
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3) Institutions with full addresses for each author: 9
1Institute of Agrochemistry and Food Technology (IATA-CSIC). Avenida Agustin 10
Escardino, 7. Paterna 46980. Valencia. Spain. 2 Instituto de Ciencia y Tecnología de 11
Alimentos (ICTA). Universidad Central de Venezuela. Caracas, Venezuela. 12
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4) name, address, telephone and fax numbers, and e-mail address of author 14
responsible for correspondence about the manuscript: 15
Cristina M. Rosell, Avda Agustín Escardino 7, 46980 Paterna, Valencia, Tel 34 16
963900022, Fax 34 963636301, E-mail: [email protected] 17
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6) the source(s) of support in the form of grants, equipment drugs, or all of these: 19
Financial support of Spanish Ministerio de Ciencia e Innovación (Project AGL 2008-20
00092 ALI and AGL2011-23802) and the Consejo Superior de Investigaciones 21
Científicas (CSIC). 22
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ABSTRACT 27
The design of gluten-free bread-like products involves the study of gluten-free dough 28
rheology and the resulting baked product characteristics, but little information has been 29
obtained connecting dough and baked product properties. The aim of this study was to 30
determine quality predictors of gluten-free bread like products at dough level by 31
defining possible correlations between dough rheological properties and both 32
instrumental parameters and sensory characteristics of the those products. Diverse rice 33
based gluten-free doughs were defined and rheologically characterized at dough level 34
and the technological and sensorial quality of the resulting baked products was 35
investigated. Dough Mixolab® parameters, bread-like quality parameters (moisture 36
content, specific volume, water activity, colour, and crumb texture), and chemical 37
composition significantly (P<0.05) discriminated between the samples tested. In 38
general, the highest correlation coefficients (r>0.70) were found when quality 39
instrumental parameters of the baked products were correlated with the dough 40
Mixolab® parameters, and lower correlation coefficients (r<0.70) were found when 41
sensory characteristics were correlated with dough rheology or instrumental parameters. 42
Dough consistency during mixing (C1), amplitude and dough consistency after cooling 43
(C5) would be useful predictors of crumb hardness; and C5 would be also predictor of 44
perceived hardness of gluten-free bread-like products. 45
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Key words: Rice flour; Gluten-free; Wheat free; Dough behaviour; Bread quality 47
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1) INTRODUCTION 50 51
Gluten-free breads are products initially designed for people who have intolerance to 52
some specific peptides comprised in the gluten proteins (Catassi & Fasano, 2008). 53
Nevertheless, there is an increasing number of people interested in wheat free foods 54
motivated by health concern or because they want to avoid wheat in the diet. 55
Particularly, gluten from wheat, rye, barley, triticale, and some varieties of oats 56
(Comino et al., 2011) must be eliminated from the diet of individuals suffering from 57
celiac disease. 58
Cereal products, especially breads, are basic components of the diet in many countries 59
due to their sensory characteristics or/and nutritional quality. However, the manufacture 60
of bread-like products without gluten results in major technological problems for 61
bakers. In fact, many gluten-free products available on the market are often of poor 62
technological quality, exhibiting low volume, poor color, and crumbling crumb, besides 63
great variation in the nutrient composition, with low protein and high fat contents 64
(Matos & Rosell, 2011). A range of bread-like gluten-free products has been designed 65
to provide coeliac disease sufferers or wheat free diet eaters with bread substitutes. The 66
term gluten-free bread is generally used for referring to a gluten-free bakery product 67
that is eaten as bread substitute, but has different characteristics than wheat bread, 68
because of that, the term gluten-free bread-like products was preferred in this 69
manuscript. The gluten-free bread recipes contain mainly rice or maize flours combined 70
with potato, maize or wheat starches (Gujral & Rosell, 2004; Gallagher et al., 2004; 71
Demirkesen et al., 2010; Matos & Rosell, 2011). 72
Rice flour is one of the most suitable cereal flours for preparing gluten-free products 73
due to its several significant properties such as natural, hypoallergenic, colorless, and 74
bland taste. In addition, it has also hypoallergenic proteins, and low content of sodium 75
and fat and high amount of easily digested carbohydrates (Gujral & Rosell, 2004). The 76
relatively small amount of prolamin in rice, forces to use some sort of gum, emulsifier, 77
enzymes or dairy products, together with rice flour, for obtaining some viscoelastic 78
properties (Demirkesen et al., 2010). Several studies had reported the use of rice flour 79
for making good-quality gluten-free bread-like products (Kadan et al., 2001; McCarthy 80
et al., 2005; Ahlborn et al., 2005; Moore et al., 2006; Lazaridou et al., 2007; Marco & 81
Rosell, 2008 a,b; Pruska-Kędzior et al., 2008; Sciarini et al., 2010; Demirkesen et al., 82
4
2010). Those studies were mainly focused on bread instrumental and/or sensory 83
characteristics. 84
Scarce information has been presented about the rheological characteristics of the 85
gluten-free doughs, which greatly vary in consistency, going from batter to dough. 86
Gluten free dough is referred to a semisolid system that can be manually handled, 87
whereas when very high water content is added in the recipe, the rheological properties 88
of the dough resemble a semiliquid system named batter. Some studies reported 89
information about gluten-free dough behavior using rheometers. Pruska et al. (2008) 90
compared the rheological properties of gluten-free dough formulations (maize flour, 91
maize starch, rice flour) concluding that they can be defined as physical gels of different 92
viscoelasticity and structural networking. Rice flour based dough or even protein 93
enriched rice flour dough behaves as a viscoelastic solid with storage modulus (G′) 94
higher than loss modulus (G″) (Gujral & Rosell 2004; Marco & Rosell, 2008b). The 95
incorporation of resistant starch increases storage (G′) and loss (G″) moduli of gluten-96
free doughs, increasing their elastic behaviour (Korus et al., 2009). Other researches 97
have studied the rheological properties of different gluten-free doughs by extrusion and 98
penetration tests using a Texture Analyzer (Moore et al., 2006; Sciarini et al., 2010; 99
Onyango et al., 2011) and the average force after reaching a plateau was used as 100
indicator of batter firmness or consistency. Rapid Visco Analyzer (Kim & Yokoyama, 101
2011) and Viscoamylograph (Sciarini et al., 2010) also gave information about the 102
pasting properties of the batters. Additionally, mixing and pasting behaviour of different 103
rice flour based doughs were studied using the Mixolab® (Marco & Rosell, 2008a). 104
Nevertheless, the information about dough or batter rheological properties has rarely 105
been exploited when designing or developing gluten-free bread like products, neither it 106
has been used for predicting bread characteristics. The main objective of this study was 107
to define predictors of the quality of gluten-free bread-like products at dough level. 108
With that aim, different gluten-free rice based doughs were defined to cover a range of 109
gluten-free doughs with different rheological features, and in consequence, to obtain 110
gluten-free bread like products with diverse technological and sensorial quality. The 111
Mixolab® was used to obtain a complete characterization of the gluten-free dough 112
behaviour by recording the mechanical changes during mixing and heating simulating 113
the mechanical work as well as the heat conditions that might be expected during the 114
baking process. Different correlations between rheological dough properties and quality 115
parameters of gluten-free bread-like products were established. 116
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117
2) MATERIALS AND METHODS 118
119
Materials 120
121
Commercial gluten-free blend (corn starch, whole egg powder, sugar, xanthan gum and 122
salt) was generously donated by Huici-Leidan SA (Huarte, Spain). Commercial rice 123
flour, supplied by Harinera Los Pisones (Zamora, Spain), had moisture and protein 124
contents of 11.5g/100g and 6g/100g, respectively. Soybean protein isolate was from 125
Trades SA (Barcelona, Spain). The soybean protein isolate had moisture, protein, lipid, 126
ash and carbohydrates (calculated by difference) contents of 6.9, 80.8, 0.2, 3.6 and 8.5 127
g/100g, respectively. Composition of the different ingredients was determined following 128
the ICC Standard Methods (1994). Corn starch, potato starch, skim milk powder and 129
whole egg powder were obtained from EPSA, (Valencia, Spain). HPMC (Methocel 130
K4M) was obtained from Dow Chemical (Pittsburg, USA). Xanthan gum food grade 131
from Jungbunzlauer (Ladenburg, Germany) has an apparent viscosity of 6.0 mPas at 132
24ºC. Pectin (GENU®pectin 150 USASAG type Baking, PKelco) was provided by 133
Puratos (Groot-Bijgaarden, Belgium). Vegetal seed oil, compressed yeast, commercial 134
sugar and salt were purchased from local market. All reagents were of analytical grade. 135
136
Mixolab® Measurements 137
138
Mixing and pasting behaviour of the gluten-free flour blends were studied using the 139
Mixolab® (Chopin, Tripette et Renaud, Paris, France), which allows mixing the dough 140
under controlled temperature and also a temperature sweep until 90ºC followed by a 141
cooling step. It measured in real time the torque (expressed in Nm) produced by passage 142
of dough between the two kneading arms, thus allowing the study of its physico-143
chemical behaviour. All ingredients used on each formulation (Table 1), with the 144
exception of yeast, were introduced into the Mixolab® bowl and mixed. The settings 145
used in the test were 8 min for initial mixing, temperature increase at 2.3 ºC/min until 146
90 ºC, 7 min holding at 90 ºC, temperature decrease at 4ºC/min until 50ºC, and 5 min 147
holding at 50ºC; and the mixing speed during the entire assay was 80 rpm. Three 148
replicates were carried out for each formulation. The following parameters were 149
obtained from the recorded curve: initial consistency (C1), stability (min) or elapsed 150
6
time at which the torque produced is kept constant, minimum torque (Nm) or the 151
minimum value of torque produced by dough passage subjected to mechanical and 152
thermal constraint (C2), peak torque (Nm) or the maximum torque during the heating 153
stage (C3), the minimum torque during the heating period (Nm) (C4) and the torque 154
obtained after cooling at 50ºC (C5). Additionally, derived parameters were calculated: 155
cooking stability range (C4-C3) and cooling setback or gelling (C5-C4). Detailed 156
description of physical changes that occurred along Mixolab® measurement (mixing, 157
pasting and gelling) was gathered by Rosell et al. (2007). Recently, detailed information 158
about Mixolab® parameters has been reported by Marco & Rosell (2008a) and Rosell et 159
al. (2010). 160
161
Breadmaking Process 162
163
Different gluten-free rice formulations were initially selected to cover a range of gluten-164
free doughs with different rheological features, and in consequence, gluten-free bread 165
like products with diverse technological and sensorial quality. Bread formulations were 166
based on reported recipes (Marco & Rosell, 2008a; McCarthy et al., 2005; Kadan et al., 167
2001; Moore et al., 2006; Pruska-Kędzior et al., 2008; Ahlborn et al., 2005; Sciarini et 168
al., 2010; Demirkesen et al., 2010), which were modified according to preliminary 169
rheological results. Seven formulations were used to obtain gluten-free bread-like 170
products (BF), one was based on corn starch (commercial blend) and in the other, rice 171
flour was the major ingredient, present individually or blended with potato or corn 172
starch. They contained different ingredients (starches, proteins, other hydrocolloids) 173
widely used in the design of gluten-free bread type products. The formulations used are 174
showed in Table 1, which were based on the following: 1000g of corn starch (F1); 175
1000g of rice flour (F2, F3); 1000g of blend of rice flour + corn and potato starches (F4, 176
F5, F6); and 1000g of blend of rice flour + potato starch (F7). Gluten-free batters or 177
doughs were prepared in a spiral mixer (AV18/2, Vimar Industries 1900, S.L., Sabadell, 178
Spain) by mixing all or part of the flour and the other ingredients with the water 179
determined in preliminary test (Table 2). Dough pieces (400g) or batters (400g) were 180
placed into regular metallic, lard coated pans and proofed in a cabinet at 85% relative 181
humidity during the time (min) and temperature (ºC) detailed in Table 2. The batter or 182
dough pieces were baked in an electric convection oven (Eurofours, Gommegnies, 183
France) as described in Table 2. After baking, loaves were removed from the pans and 184
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kept at room temperature for 2 hours to cool down. Loaves packed in polyethylene bags 185
to prevent drying were stored at 24 ºC for 24 hours and then used for bread quality 186
assessment. Four loaves were obtained from each formulation. Duplicates were carried 187
out in different days. 188
189
Quality Assessment of Gluten-free Bread-like Products 190
191
Instrumental quality parameters 192
193
The moisture content of gluten-free bread-like samples was determined following the 194
ICC (1994). Volume was determined by the rapeseed displacement method. Specific 195
volume (cm3 /g) of the individual loaf was calculated by dividing volume by weight. 196
Water activity of samples was measured using an Aqua Lab Series 3 (Decagon devices 197
Pullman, USA) at 22ºC. The colour of the crumb samples was measured at three 198
different locations by using a Minolta colorimeter (Chromameter CR-400/410, Konica 199
Minolta, Tokyo, Japan) after standardization with a white calibration plate (L*= 96.9, 200
a*= -0.04, b*=1.84). The colour was recorded using CIE-L*a*b* uniform colour space 201
(CIE-Lab) where L* indicates lightness, a* indicates hue on a green (-) to red (+) axis, 202
and b* indicates hue on a blue (-) to yellow (+) axis. Data from three slices per sample 203
were averaged. 204
The crumb hardness was measured on uniform slices of 10mm thickness. Three slices 205
from the centre of each loaf were used for texture evaluation. Texture profile analysis 206
(TPA) was performed using a universal testing machine TAXT2i (Stable Micro 207
Systems, Surrey, UK) equipped with a 30-Kg load cell and 25-mm aluminium 208
cylindrical probe. Crumb characteristics were assessed using a texture analyser 209
(TAXT2i texture analyser Stable Micro Systems, Surrey, UK). The settings used were a 210
test speed of 2.0 mm/s with a trigger force of 5 g to compress the middle of the bread 211
crumb to 50% of its original height at a crosshead speed of 1mm/s. Values were the 212
mean of at least three replicates. 213
214
Chemical Composition 215
216
The chemical composition of the samples was determined according to ICC 217
corresponding standard methods (ICC, 1994), namely, the moisture content (ICC 218
8
standard 110/1), fat (ICC 136), proteins (N x 6.25) (ICC 105/2) and ash (ICC 104/1). 219
Total carbohydrates were determined by difference subtracting 100 g minus the sum of 220
protein, ash and fat expressed in grams/100 grams FAO (2003). Determinations were 221
carried out in triplicate. 222
223
Sensorial Analysis 224
225
A descriptive sensory analysis was performed for evaluating the sensory characteristics 226
of the gluten-free bread-like products. Sensory analysis was carried out with ten trained 227
panellists under normal lightening conditions and at room temperature. The range of 228
time that the test panellist had participated in descriptive analysis and scale rating of a 229
wide range of bread products varied from 3 to 20 years. Samples were presented in 230
slices (1cm thick) on plastic dishes coded and served in a randomised order. Preliminary 231
training test was performed to define the best descriptors for characterizing the product. 232
Panellists were sat in a round table and after evaluating the sample, an open discussion 233
was initiated to define the best descriptors for characterizing the product. Evaluation 234
included perception at first glance of the bread slice (crust and crumb included) and 235
mastication with the molar teeth up to swallowing. The attributes assessors finally agree 236
were, appearance (by observing the product slice), odour, colour, taste, texture attributes 237
during chewing and springiness (ability to regain original shape after pressing down the 238
crumb with the middle finger). The descriptors for each attributes were appearance 239
(visually liking or disliking), odour (scale goes from high when typical of bread or 240
bakery products to low, uncharacteristic of bakery products), colour (scales goes from 241
high yellow/beige to low when brown or grey), taste (scale goes from high when typical 242
taste of bread or bakery products to low, uncharacteristic of bakery products), texture 243
attributes during chewing (scales goes from hard-soft, crumbly-cohesive). Attribute 244
intensity was scored on a scale varying from 1 to 5. Samples were considered 245
acceptable if their mean score for overall acceptance was above 3.0 (neither like nor 246
dislike). 247
248
Statistical Analysis 249
250
For each quality parameter, a one way analysis of variance (ANOVA) was applied using 251
Statgraphics Plus V 7.1 (Statistical Graphics Corporation, UK). Fisher’s least significant 252
9
differences (LSD) test was used to assess significant differences (P<0.05) among 253
samples that might allow discrimination among them. Additionally, Pearson correlation 254
analysis was applied to establish possible relationships between the rheological dough 255
properties and both instrumentals and sensorial quality parameters of the gluten-free 256
bread-like products. 257
258
3) RESULTS AND DISCUSSION 259
260
Mixing and Pasting Properties of Gluten-free Doughs 261
262
Figure 1 show the curves obtained from the Mixolab® corresponding to the seven 263
gluten-free dough formulations evaluated. Plots reflected the dough changes due to both 264
the mixing force and the temperature. The patterns obtained during mixing, overmixing, 265
pasting and gelling greatly varied with the mixture composition, which was expected 266
considering the complex blend of ingredients (Table 1). The presence of different 267
proteins and starches modifies protein-protein interactions and also the starch 268
gelatinization and the gelling processes (Rosell et al., 2007; Marco & Rosell, 2008a; 269
Rosell et al., 2010). All Mixolab® parameters significantly (P<0.05) discriminated 270
among the formulated dough tested (Table 3). During the mixing and overmixing, 271
significant variation was observed in the dough maximum consistency, time to reach 272
that consistency and the stability (Table 3). Some formulations yielded mixtures with 273
dough consistencies (with C1 higher than 0.5 Nm), whereas F3, F4, F5 and F7 led to 274
mixtures with batter consistencies (C1 lower than 0.3 Nm) that were difficult to handle. 275
F6 showed the highest C1 value and the lower time to C1 value, indicating that this 276
dough reached major consistency in minor time, likely due to its major amount of 277
proteins (egg, milk). Regarding stability, F7 showed the highest value followed by F1, 278
while F5 presented the lower dough stability value. The amplitude, indicative of the role 279
of water in the lubrication during mixing (Rosell & Collar, 2009) showed also 280
significant differences, and thus different extensional properties of the evaluated 281
doughs. The simultaneous mechanical shear stress and temperature led to a minimum 282
torque that has been related to protein unfolding or protein weakening (Rosell et al., 283
2007). The values for C2 were quite low compared with the ones detected for wheat 284
dough (0.4-0.5 Nm). That result might be ascribed to the protein thermal properties 285
rather than to the amount of proteins, since some gluten-free doughs had very high 286
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protein content (F4 and F6). As temperature increases, starch gelatinization occurs and 287
therefore viscosity increases, which is detected as an increase in torque (Rosell et al., 288
2007). As was expected F1 showed the highest C3 value, likely due to its highest starch 289
content, specifically corn starch (Table 1). In the case of F2 and F3 (only with rice flour 290
as starch source), a delayed peak corresponding to starch gelatinization was observed, 291
derived from the high gelatinization temperature of the rice starch. It should be 292
remarked that two gelatinization peaks were observed in F4, F5 and F6. Those peaks 293
resulted from the presence of different starches (rice, corn and potato) with diverse 294
pasting temperatures, being 65.4ºC for potato starch, 69.9ºC for corn starch and 70.2ºC 295
for rice flour. Furthermore, it must be taken into account that hydrocolloids like xanthan 296
gum, HPMC or pectin, contained in the doughs can retain water, competing with the 297
starch for the available water, limiting the starch granule swelling and, therefore 298
promoting a delay in the pasting process (Rosell et al., 2011). 299
During temperature holding at 90ºC, a reduction in consistency occurred, which is 300
related to the physical breakdown of the starch granules. F1 showed the highest value, 301
likely due to the high content of corn starch in this dough. 302
After cooling, F1 presented the highest C5 value followed by F6 and F5. The cooling 303
process was accompanied by an enhancement of dough consistency associated to starch 304
gelling, due to amylose chains crystallization, which is greatly dependent on the starch 305
type and the presence of gelling additives or ingredients with water binding ability 306
(Rosell et al., 2007; Rosell et al., 2010). Regarding the secondary parameters, all doughs 307
showed very low cooking stability range (C4-C3); whereas the cooling setback (C4-C5) 308
was only significantly higher for F1 and F6 (Table 3). High setback value suggests that 309
dough presents high retrogradation tendency and, consequently the baked product 310
prepared from this dough would undergo high staling rate over storage. 311
Some studies have been published about the effect of gelling agents and proteins on the 312
mechanical properties of wheat dough due to dual mixing and temperature constraint 313
using the Mixolab® (Collar et al., 2007; Marco & Rosell, 2008a, Rosell & Collar, 2009; 314
Rosell et al., 2010). Those studies concluded that the effect of gelling or thickening 315
agents on the mechanical properties greatly depends on the nature of the added polymer 316
and the type of interaction among them. Moreover, the addition of proteins to wheat or 317
rice flour also led to changes on the mechanical and baking properties, depending on the 318
protein source (Bonet et al., 2006; Marco & Rosell, 2008a). 319
320
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Bread Quality Assessment 321
322
Gluten-free bread-like products (BF1-BF7) obtained from the formulated doughs (F1-323
F7) presented important crumb differences regarding colour, appearance, shape, size 324
and volume. The values obtained for specific volume, crumb colour, moisture content, 325
water activity, height/width ratio and hardness are showed in Table 4. All instrumental 326
quality parameters tested significantly (P<0.05) discriminated among samples. Specific 327
volume values ranged from 1.44 to 3.03 cm3/g, except for BF2 (4.48 cm3/g) and BF7 328
(5.07 cm3/g), which showed the highest values of specific volume. In general, values of 329
specific volume obtained in this study agree with previous reports (Hathorn et al., 2008, 330
Marco & Rosell, 2008a; Sabanis et al., 2009, Sciarini et al., 2010). 331
The L*, a* and b* values for crumb colour showed significant (P<0.05) differences 332
among gluten-free bread-like products (Table 4). The lower values of L* (lightness) 333
were obtained for BF4 and BF6, which had in common the presence of xanthan gum, 334
and proteins blend (soybean protein in BF4 or skim milk powder and whole egg powder 335
in BF6). Likely, soybean proteins and egg powder could be responsible of decreasing 336
lightness, since BF7, containing only skim milk powder as protein source showed the 337
highest L* value. Regarding a*, all showed negative (green hue) values, with exception 338
of BF6. The b* scale showed positive value (yellow hue) for all samples evaluated. BF6 339
exhibited significantly higher b* value than the other samples, derived from the original 340
yellow pigment of the egg powder added as ingredient in this formulation. 341
Significant differences (P<0.05) in crumb moisture and water activity were found 342
among the different gluten-free bread-like samples (Table 4). Differences in water 343
activity and moisture content could be attributed to differences in the recipes. In fact, 344
BF6 showed the lowest water activity and moisture content, which can be ascribed to 345
the presence of whole egg powder in the formulation. The highest moisture content was 346
observed in BF4 that contained soy protein, which agrees with results of Marco & 347
Rosell (2008a) when incorporating soybean proteins to gluten-free breads. Overall, the 348
crumb moisture contents were lower than those reported by other researchers (Sabanis 349
et al., 2009; Marco & Rosell 2008a; Matos & Rosell, 2011). 350
Wide variation in the crumb hardness (1.3 N to 147.5 N) was observed among the 351
gluten-free bread-like samples (Table 4). These results reflect large differences 352
depending on type of formulation used for obtaining the experimental gluten-free baked 353
products. Frequently, gluten-free bread-like products due to their complex formulation, 354
12
mainly based in carbohydrates (Matos & Rosell, 2011), present high crumb hardness 355
when compared to standard wheat bread. 356
Table 5 shows the macronutrients compositions of the seven gluten-free bread 357
specialities evaluated in this study. Analysis of data collected using ANOVA showed 358
that all chemical composition significantly (P<0.05) discriminated between the baked 359
samples. Protein and fat content ranged between 3.30-14.97 g/100g, and 0.20-9.57 360
g/100g, respectively. In regard to protein content, it was high in the gluten-free bread-361
like samples BF4 and BF6 which contained more proteins, while BF6 and BF7 were the 362
specialties with higher fat content. Total carbohydrate was the major component in 363
gluten-free bread-like products based on flours and/or starches. These results agree with 364
those recently reported by Matos & Rosell (2011) who evaluated in detail the chemical 365
composition of many types of gluten-free bread like products. 366
Sensory analysis of the different types of gluten-free bread-like samples is presented in 367
Table 6. According to ANOVA results, these bread-like products differed significantly 368
(P<0.05) in crumb appearance, taste, colour, springiness, hardness and crumbliness. 369
Conversely, no significant differences were observed in odour. The highest score for 370
crumb appearance, colour and perceived hardness was obtained for BF3 and BF5. 371
Additionally, the best taste was perceived in BF3, and BF5 received the highest score 372
for springiness, indicating major elasticity. In general, BF3, which did not contain any 373
additional protein source, was scored high for most of the sensorial attributes evaluated, 374
including hardness and crumblines. On the contrary, BF6 was scored low for most of 375
the sensory attributes evaluated. It seems that the addition of whole egg powder as 376
unique source of proteins affected negatively the sensory perception of this product. The 377
results obtained from sensory test clearly revealed great variability on sensory quality of 378
the gluten-free bread-like products tested. 379
380
Relationships among the Rheological Properties of Formulated Doughs and the 381
Instrumental and Sensory Characteristics of the Gluten-free Bread-like Products 382
383
Relationship among the rheological properties of formulated doughs recorded from 384
Mixolab®, and the product instrumental and sensory characteristics were analyzed. 385
Table 7 illustrates the broad range of correlations found between parameters obtained 386
during the heating and cooling cycles with the Mixolab® and the instrumental quality 387
parameters (specific volume, water activity, moisture content and TPA-hardness) of the 388
13
bread-like baked products. Water activity and moisture content were highly significant 389
and negatively correlated with C1, amplitude and gelling (C5-C4) parameters. Specific 390
volume showed high and negative correlation with cooking stability range (C4-C3) and 391
C5 parameters, which are associated to the cooling stage of the Mixolab®. Presumably, 392
high dough or batter consistencies limit the expansion during proofing, reducing the 393
specific volume. Nevertheless, a positive correlation between apparent viscosity and 394
loaf volume (r = 0.83, P<0.05) and also between porosity and loaf volume values (r = 395
0.81, P <0.05) in gluten-free breads has been reported by Sabanis et al., (2009). There 396
were good correlations between TPA-hardness values and Mixolab® parameters. The 397
relationships between the TPA-hardness and C1, amplitude, C5 and gelling (C5-C4) 398
parameters were found to be particularly highly significant (P <0.001) and positive. 399
This could indicate that the TPA-hardness values are strongly correlated (r >0.70) with 400
parameters characterising both protein and starch cooling behaviours. It is important to 401
remark that wheat dough viscosity characteristics determined with the Rapid 402
Viscoanalyzer (RVA) have been also correlated with wheat bread texture parameters 403
(Collar 2003). The pasting profile during cooking and cooling of wheat dough has been 404
highly correlated with bread staling kinetic parameters. Particularly, peak viscosity, 405
pasting temperature, and setback during cooling can be considered predictors at dough 406
level of bread firming behaviour during storage of wheat bread. Regarding gluten-free 407
doughs, pasting behaviour of corn flour has been significantly correlated with dough 408
textural parameters. Specifically, springiness and stickiness parameters were positively 409
associated to gelatinisation and retrogradation phenomena (Brites et al., 2010). 410
Table 8 showed correlation coefficients and significance levels found among Mixolab®411
parameters, instrumental quality parameters and sensory characteristics obtained from 412
formulated dough and the prepared gluten-free bread like products. Particularly, all 413
sensory characteristics evaluated (appearance, colour, springiness, hardness and 414
crumblines) showed significant negative correlations with b* (hue on a yellow axis), 415
although correlation coefficients only indicated strong linear relationship between b*416
and perceived colour and perceived hardness. It seems that crumb structure has strong 417
influence on the b* parameter. Additionally, hardness perceived revealed high (P418
<0.001) and positive correlation with specific volume (r = 0.7149) and high negative 419
correlations with b* (r = -0.7945), TPA-hardness (r = -0.7646) and C5 (r = -0.7005) 420
Mixolab® parameter. 421
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Hardness is a very important sensory characteristic when assessing bread quality. In this 422
study, as it was mentioned, perceived hardness showed negative correlation with b* and 423
TPA-hardness. Apparently, the colour perception is closely related to crumb structure 424
since breads presenting hue yellowness and packed crumb structure could be rated 425
lowly. It has been reported that smaller loaves were denser and had tightly packed 426
crumb structure, resulting in higher crumb firmness (Sabanis et al., 2009); this drives to 427
think that bread with compact crumb could be perceived as hard. Sabanis et al. (2009) 428
reported a negative correlation between crumb firmness and loaf volume (r = -0.89, P429
>0.05). 430
In general, many relationships were found (Table 8), however the correlation 431
coefficients were higher between dough properties and instrumental bread parameters (r 432
>0.70) than among instrumental parameters and sensory characteristics (r <0.70). 433
434
4) CONCLUSIONS 435
436
The patterns obtained during mixing, overmixing, pasting and gelling greatly varied 437
depending on the gluten-free dough or batter composition. All Mixolab® parameters 438
significantly (P<0.05) discriminated among the doughs evaluated. Additionally, 439
differences found in the rheological dough properties from Mixolab® were mainly 440
associated with the presence/ absence of protein and starch sources in the dough. 441
Instrumental quality parameters evaluated in the gluten-free bread-like products 442
significantly (P <0.05) discriminated among the samples. 443
Several relationships were found among the rheological properties of formulated gluten-444
free dough/batter, the instrumental quality parameters and sensory characteristics of the 445
bread-like products. In general, the highest correlation coefficients (r >0.70) were 446
obtained between the Mixolab® rheological properties at dough level and the 447
instrumental quality parameters of the fresh baked products. Conversely, lower 448
correlation coefficients (r <0.70) were found when correlations were established with 449
sensory characteristics. Particularly, dough/batter consistency during mixing (C1), 450
amplitude and dough consistency after cooling (C5) would be useful predictors of TPA 451
crumb hardness of baked product; and C5 would be also predictor of perceived hardness 452
of gluten-free bread-like products. 453
454
5) ACKNOWLEDGMENTS455
15
Authors acknowledge the financial support of Association of Coeliac Patients 456
(Madrid, Spain), Spanish Scientific Research Council (CSIC) and the Spanish 457
Ministry of Economy and Sustainability (Project AGL2008-00092/ALI and 458
AGL2011-23802). M.E. Matos would like to thank predoctoral grant by the Council 459
of Scientific and Humanistic Development of University Central of Venezuela 460
(Caracas, Venezuela).461
462
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543
544
Figure Captions545
Figure 1. Plots obtained with different gluten-free doughs/batters when recording the 546
rheological behaviour by using Mixolab® device. 547
548
549
18
Table 1 Gluten-free dough formulations
+ Ingredient present in the commercial blend
Ingredients F1 F2 F3 F4 F5 F6 F7
Commercial GF blend, g 1000 - - - - - - Rice flour, g - 1000 1000 350 400 696 500 Corn starch + - - 225 200 130 - Potato starch - - - 300 400 174 500 Fresh yeast, g 50 30 28 20 50 22 50 Salt, g - 18 24 17 15 17 20 Sugar, g 10 30 120 10 60 78 50 Vegetal oil, g - 60 56 - 30 52 60 Skim milk powder, g - - - - - 39 100 Whole egg powder, g + - - - - 174 - Soy protein, g - - - 125 - - - Xanthan gum, g + - - 10 - 16 - HPMC, g - 40 28 - - 4 22 Pectin, g - - - - 50 - - Water (mL) 600 1100 1060 1050 900 565 790
19
Table 2 Breadmaking process conditions for each gluten-free dough formulations
Breakmaking F1 F2 F3 F4 F5 F6 F7 Mixing Procedure Mix all
ingredients a) Mix 500g rice flour with 550ml boiling water for 5min, cool down till 35ºC. b) Add the rest of ingredients
a) Mix water, rice flour and oil b) Mix other dry ingredients c) Mix (a+b)
a)Mix yeast in a solution of sugar and water b)Add the rest of ingredients
Mix all ingredients
a)Mix yeast in a solution of sugar and water b) Add slowly xanthan gum and HPMC during 3min mixing c) Add rest of ingredients
a)Mix yeast with water and then oil b) Mix dry ingredients for 1 minc) Mix a+b
Time (min) 5 5 10 10 3 5 (then hold 10 min), 3 2
Fermentation Time (min) 45 60 40 30 40 50 35
Temperature (ºC) 30 30 35 30 35 30 40
Baking Time (min) 25 60 45 45 30 50 25Temperature (ºC) 210 175 190 190 200 190 230
20
Table 3 Rice-based dough characteristics during mixing and heating determined by using the Mixolab®
F1 1.37±0.05 bc 0.88±0.10 d 2.49±0.30 e 0.07±0.01 b 0.33±0.01 b 3.07±0.03 e 2.99±0.04 d 3.64±0.6 e -0.08±0.00 d 0.65±0.05 dF2 1.79±0.03 c 0.56±015 c 0.51±0.08 b 0.07±0.00 b 0.22±0.01 b 0.87±0.01 b 0.65±0.06 ab 0.84±0.08 a -0.22±0.00 b 0.19±0.02 aF3 1.01±0.10 ab 0.14±0.20 ab 1.29±0.15 d 0.01±0.00 a 0.01±0.00 a 0.69±0.05 a 0.56±0.07 a 0.74±0.07 a -0.13±0.00 c 0.18±0.02 aF4 1.70±0.11 c 0.05±0.18 a 1.00±0.21 c 0.01±0.00 a 0.02±0.01 a 0.77±0.03 ab 0.70±0.04 b 1.00±0.05 b -0.08±0.00 d 0.30±0.05 bF5 0.75±0.19 a 0.14±0.15 ab 0.09±0.13 a 0.04±0.02 ab 0.01±0.00 a 1.05±0.07 c 1.03±0.05 c 1.45±0.04 c -0.02±0.00 e 0.42±0.05 cF6 0.67±0.21 a 1.77±0.13 e 0.48±0.03 b 0.29±0.01 c 0.23±0.01 b 1.30±0.06 d 1.07±0.03 c 2.61±0.07 d -0.23±0.01 b 1.54±0.06 eF7 1.03±0.15 ab 0.26±0.09 b 5.46±0.27 f 0.02±0.01 a 0.00±0.00 a 1.15±0.05 c 0.57±0.03 a 1.00±0.06 b -0.58±0.02 a 0.43±0.04 c
p-value 0.0024 0.0000 0.0000 0.0000 0.0003 0.0000 0.0000 0.0000 0.0000 0.0000
Gelling, C4-C3, NmDough Codes
Cooking stability range,C4-C3, NmC4, Nm C5, NmC3, NmAmplitude, Nm C2, NmC1, Nm Stability, minTime to C1, min
Values are means ± standard deviation. Different letters within a column mean significant differences (P<0.05). C1: initial consistency; C2: minimum torque; C3: maximum torque during the heating; C4: minimum torque during the heating period; C5: torque obtained after cooling at 50ºC.
21
Table 4 Instrumental quality parameters of the gluten-free bread-like products
Values are means ± standard deviation. Different letters within a column mean significant differences (P<0.05). TPA-Hardness: Crumb hardness measured with a texturometer.
Crumb colour parameters Samples codes
Specific Volume,
cm3/g L* a* b*
Moisture content,
% Water activity
TPA-Hardness, N
BF1 1.91 ± 0.05 b 78.31 ± 0.76 d -2.59 ± 0.17 a 14.47 ± 0.79 d 37.17 ± 0.07 c 0.96 ± 0.00 c 84.90 ± 3.07 cBF2 4.48 ± 0.02 f 72.17 ± 1.01 c -1.21 ± 0.20 bc 7.13 ± 1.02 b 37.97 ± 0.04 d 0.96 ± 0.00 c 1.33 ± 0.33 aBF3 3.03 ± 0.04 e 73.79 ± 2.87 c -0.89 ± 0.16 cd 6.30 ± 0.25 b 37.40 ± 0.17 c 0.95 ± 0.00 b 2.30 ± 0.30 aBF4 2.52 ± 0.04 d 62.24 ± 0.81 a -0.80 ± 0.15 d 12.15 ± 0.54 c 43.53 ± 0.32 f 0.97 ± 0.00 d 36.27 ± 2.93 bBF5 2.41 ± 0.04 c 65.77 ± 0.27 b -1.22 ± 0.02 bc 5.06 ± 0.12 a 39.30 ± 0.08 e 0.97 ± 0.00 d 7.53 ± 0.46 aBF6 1.44 ± 0.03 a 63.40 ± 0.62 a 1.72 ± 0.43 e 21.89 ± 0.37 e 25.67 ± 0.30 a 0.92 ± 0.00 a 147.50 ± 11.12 dBF7 5.07 ± 0.08 g 81.50 ± 0.09 e -1.53 ± 0.04 bc 6.47 ± 0.15 b 33.33 ± 0.06 b 0.95 ± 0.00 b 5.43 ± 0.51 aP- value 0.000 0.000 0.000 0.000 0.000 0.000 0.000
22
Table 5 Proximate composition of the gluten-free bread-like products.
(*)Total Carbohydrate (dm) by difference: 100 – (weight in grams [protein + fat + ash] in 100 g of food) (FAO. 2003).
Values are means ± standard deviation. Different letters within a column mean significant differences (P<0.05).
SampleCodes
Protein, g/100g, dm
Fat, g/100g, dm
Minerals, g/100g, dm
Total Carbohydrate*g/100g, dm
BF1 3.30 ± 0.00 a 0.97 ± 0.02 b 1.37 ± 0.12 bc 64.87 ± 0.16 gBF2 7.57 ± 0.12 e 3.40 ± 0.01 d 1.13 ± 0.08 a 55.57 ± 0.08 c BF3 7.10 ± 0.04 c 3.70 ± 0.00 e 1.31 ± 0.00 b 54.57 ± 0.18 bBF4 14.97 ± 0.00 g 0.20 ± 0.02 a 1.47 ± 0.03 c 43.90 ± 0.31 a BF5 3.63 ± 0.03 b 1.87 ± 0.01 c 1.03 ± 0.06 a 58.20 ± 0.06 f BF6 12.33 ± 0.03 f 9.57 ± 0.00 g 1.46 ± 0.01 c 56.17 ± 0.29 d BF7 7.43 ± 0.03 d 4.77 ± 0.04 f 1.41 ± 0.14 bc 57.43 ± 0.17 e
P- value 0.0000 0.0000 0.0001 0.0000
23
Table 6 Sensorial analysis of the gluten-free bread like products
Values are means ± standard deviation. Different letters within a column mean significant differences (P<0.05)
SampleCodes
Crumbappearance Taste Odour Colour Springiness Hardness Crumblines
BF1 2.67 ± 1.21 bc 1.33 ± 0.52 a 2.17 ± 1.17 3.00 ± 0.89 bc 1.50 ± 1.22 a 1.50 ± 1.22 a 1.67 ± 0.82 a BF2 2.67 ± 0.52 bc 2.50 ± 0.84 b 3.17 ± 0.75 3.67 ± 1.03 bc 1.33 ± 0.52 a 3.83 ± 0.75 b 3.67 ± 1.37 bcBF3 4.50 ± 0.55 d 3.67 ± 1.14 c 3.33 ± 1.48 4.33 ± 0.45 c 2.00 ± 0.71 ab 4.17 ± 0.84 b 4.00 ± 1.00 c BF4 1.33 ± 0.89 a 1.17 ± 0.45 a 1.83 ± 0.84 2.67 ± 0.89 ab 3.00 ± 1.87 bc 2.00 ± 1.22 a 1.33 ± 0.55 a BF5 4.50 ± 0.55 d 2.50 ± 0.55 b 3.33 ± 1.03 4.33 ± 0.82 c 3.33 ± 1.03 c 3.67 ± 0.52 b 2.17 ± 0.75 abBF6 1.83 ± 1.17 ab 2.50 ± 0.84 b 2.33 ± 1.21 1.67 ± 0.82 a 1.17 ± 0.41 a 1.50 ± 0.84 a 1.50 ± 0.84 a BF7 3.17 ± 0.41 c 3.33 ± 1.21 bc 2.83 ± 1.33 3.67 ± 1.21 bc 2.33 ± 1.37 abc 4.33 ± 1.21 b 3.00 ± 0.63 bcP-value 0.0000 0.0000 0.1218 0.0002 0.0089 0.0000 0.0000
24
Table 7 Correlation matrix between instrumental quality parameters of gluten-free bread-like products and dough/batter rheological parameters determined with the Mixolab®
Correlations indicated by r values. ***P-value <0.001, **P-value <0.01, *P- value <0.05. C1: initial consistency; C2: minimum torque; C3: maximum torque during the heating; C4: minimum torque during the heating period; C5: torque obtained after cooling at 50ºC.
Instrumental quality parameters
Mixolab® parameters Specific volume Water activity Moisture content TPA-Hardness
Time to C1 0.5101* 0.5422*C1 -0.4816* -0.7833*** -0.8193*** 0.8969***Stability 0.5579**Amplitude -0.5151* -0.7768*** -0.8113*** 0.8671***C2 0.5916** C3 0.4880* C4 -0.5112* 0.4868* C5 -0.6594** 0.7849***Cooking stab range C4-C3 -0.7016*** 0.4749*Gelling C5-C4 -0.5906** -0.8013*** -0.8355*** 0.9287***
25
Table 8 Correlation matrix between sensory characteristics and instrumental parameters at dough and baked product level
Sensorial characteristicsInstrumental parameters Crumb appearance Colour Springiness Hardness Crumblines
Mixolab® parametersC1 -0.6494** -0.571**Amplitude -0.5182* -0.5444*C2 -0.6232** -0.5332*C3 -0.5179*C4 -0.5639**C5 -0.7005*** -0.5584**Gelling C5-C4 -0.5913** -0.5217*
Quality parametersSpecific volume 0.7149*** 0.6242**L* 0.4852*a* -0.4737*b* -0.6073** -0.7636*** -0.4398* -0.7945*** -0.6071**Water activity 0.5362*Moisture content 0.5403*TPA-Hardness -0.4904* -0.4375* -0.7646*** -0.6102**
Correlations indicated by r values. ***P-value <0.001, **P-value <0.01, *P- value <0.05. C1: initial consistency; C2: minimum torque; C3: maximum torque during the heating; C4: minimum torque during the heating period; C5: torque obtained after cooling at 50ºC.
26
Figure 1.
